This invention relates to steam cooking of food products and, more particularly, to industrial high-volume cookers continuously conveying food products, such as thick layers of vegetables, through a cooking chamber on a flighted foraminous conveyor belt through which jets of steam are directed.
Steam cookers through which conveyor belts carry food products are well known. For example, skins are loosened on tomatoes carried on a conveyor belt in Ryder, U.S. Pat. No. 1,992,398, Feb. 26, 1935 by maintaining a cooking zone of superheated steam at above atmospheric pressure. There is no attempt to efficiently cook the entire product, nor to produce an efficient cooker. Thus, the hot steam at high pressure is used to purge air out of the cooking zone and thus the steam energy is inefficiently used for cooking the food.
Vegetables are steam cooked by vaporized water over a body of boiling water in Bichel, U.S. Pat. No. 4,937,090, Jun. 26, 1990. The lower cooking temperatures, criticality in temperature and product controls, and inefficiency of heat exchange between the product and heating medium encompass a long cooking time and prevents uniformity and efficiency of cooking from the energy source that heats the water tank.
Ellis-Brown, U.S. Pat. No. 5,072,663, Dec. 17, 1991, specially teaches a cooker for shrimp with steam flowing at a pressure higher than atmospheric through a cooking zone containing a conveyor belt. Input cooking steam is mixed with air carried into the compartment by the belt, and vapors released by the cooking shrimp before reaching the shrimp cooking region, so that the input steam energy is not concentrated and spent solely upon the shrimp being cooked. Furthermore, uniform cooking conditions are difficult to obtain because of dependency upon variable air temperature and humidity, for example. Also, hotter steam migrating to the top of the compartment is discharged out of the top of the cooker to further decrease cooking efficiency. The incoming steam pressure keeps the compartment above atmospheric pressure, thus further tending to force the hot steam out into the atmosphere. Since an attempt is made to conserve minor energy losses through cabinet walls with specially formed insulation of stainless steel housing, it is clear that a more efficient system was not recognized.
A previous development is a saturated steam cooker in the George C. Lapeyre et al. U.S. Pat. No. 4,862,794, Sep. 5, 1989, for APPARATUS FOR CONTROLLING PRECOOKING AND MACHINE PEELING SHRIMP. This cooker carries shrimp on a conveyor into a shallow inverted open bottom box into which is continuously fed saturated steam near the closed top panel where it remains until condensation descends into the atmosphere through the open bottom as it cools from the cooking of shrimp on the conveyor belt by saturated steam at the constant temperature of 212.degree. F. Thus, as long as the saturated steam is replenished as needed to replace cooking energy for the amount of shrimp cooked in its presence, the cooking temperature remains constant. There is a significant advantage in keeping air and vapors from the saturated steam by the flow of fresh saturated steam into the cooking region. In addition to decreasing cooking efficiency, air and vapors carry oxygen, which reacts with the cooking product, whether shrimp or vegetables, to degrade the quality and appearance (i.e., taste and color) of the cooked product.
This prior art cooker works well, but has been found to have operational deficiencies which are resolved by the present improved cooker. For example, the shallow open bottom box structure permits the escape of enough hot steam to reduce cooking efficiency. Also, a shallow open bottom container for confining saturated steam permits entry of contaminants such as air or internal vapors in response to external and internal air flow paths. For example, if in the vicinity of cross winds from an open window or heater duct in a plant, the retention of uncontaminated saturated steam in the cooking region necessary for cooking efficiency and repeatable cooking quality control is not feasible.
Furthermore, the cooking of various sizes of shrimp at differing input temperatures and moisture content, etc., when carrying various loading densities of raw shrimp in industrial quantities on a movable conveyor belt through the cooker imposes a wide range of cooking conditions. The prior art cookers could not handle efficiently such wide ranges of conditions encountered in practice with efficient cooking methods at high volume industrial capacity where cooking speeds must be high without deterioration of consistent product quality under simple and effective automatic control conditions. For example, the shallow height of the cooking chamber in the Lapeyre et al. cooker makes it difficult to maintain control under varying thermal product loads.
Thus this invention has as an objective the improvement of the state of the art by providing an improved automatically controlled cooking chamber with internal pressure substantially atmospheric that prevents dilution or variation of the 212.degree. F. cooking energy of saturated steam surrounding the product being cooked.
Further, it is a general objective of the present invention to provide more efficient and uniform cooking methods and equipment adapted to higher volume, higher speed industrial use.
The aforementioned objectives are met by the high efficiency steam cooker first described and claimed in related U.S. Pat. No. 5,184,538 to Ledet. Nevertheless, the high-volume cooking or blanching of thick or dense layers, or mats, of vegetables presents a problem for conventional steam cookers. In particular, it is difficult to cook uniformly a thick mat of vegetables conveyed through a steam cooking chamber in a high-volume industrial application, while simultaneously maintaining an oxygen-free saturated steam cooking environment.
Thus, yet another objective of the invention is to provide means for uniformly cooking food products conveyed in a thick mat into a steam cooking chamber.